1. Field
The present application relates generally to light emitting diodes, and more particularly, to a system for wafer-level phosphor deposition.
2. Background
A light emitting diode comprises a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, a doped region of the semiconductor can have predominantly electrons or holes, and is referred to as an n-type or p-type semiconductor region, respectively.
In LED applications, an LED semiconductor chip includes an n-type semiconductor region and a p-type semiconductor region. A reverse electric field is created at the junction between the two regions, which causes the electrons and holes to move away from the junction to form an active region. When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and combine. When electrons combine with holes, they fall to lower energy levels and release energy in the form of light. The ability of LED semiconductors to emit light has allowed these semiconductors to be used in a variety of lighting devices. For example, LED semiconductors may be used in general lighting devices for interior applications or in various exterior applications.
During manufacture, a large number of LED semiconductor dies are produced on a semiconductor wafer. For example, the wafer may comprise one hundred or more dies. A process referred to as singulation is used to cut the dies from the wafer. The dies may then be coated with a phosphor coating that controls the color of the light emitted from the die when energized. After coating, the dies are probed and tested for color, light intensity output, power consumption and any other types of operational characteristics.
Unfortunately, coating and testing the dies after singulation may be expensive or complicated and make it difficult to obtain dies having consistent color, light intensity output, or other characteristics.
Accordingly, what is needed is a simple and efficient way to apply a phosphor coating on a semiconductor wafer and perform testing prior to singulation to achieve consistent die characteristics and to avoid the expensive and complicated process of working with individual dies.